Field of the Invention
The present invention relates to an inspection apparatus such as an ophthalmic imaging apparatus to be used in ophthalmologic diagnosis and treatment, an image processing apparatus, a method of operating an inspection apparatus, an image processing method, and a recording medium.
Description of the Related Art
Scanning laser ophthalmoscopes (hereinafter referred to as “SLO apparatus”), which are ophthalmic imaging apparatuses utilizing the principle of confocal laser microscopes, are configured to perform raster scan on the fundus of an eye with laser light serving as measuring light to quickly acquire a two-dimensional image of the fundus of the eye that is high in resolution from the intensity of return light of the measuring light.
In SLO apparatus, the measuring light needs to form a minute spot on the fundus of the eye in order to improve lateral resolution. It is, however, difficult to improve resolution by simply increasing the beam diameter of the measuring light, due to the distortion of the spot shape from aberrations of the measuring light and the return light thereof that are caused on the eye being inspected.
To solve this, adaptive optics SLO apparatuses (hereinafter referred to as “AO-SLO apparatus”) have been developed in recent years which incorporate an adaptive optics system configured to measure aberrations by the eye that is being inspected and to compensate for aberrations of the measuring light and the return light thereof that are caused on the eye being inspected, with the use of a wavefront compensation device. The development has made acquiring a two-dimensional image (AO-SLO image) high in resolution a realistic possibility.
On the other hand, for some site or tissue of the fundus of the eye whose image is to be acquired, a two-dimensional image is acquired by intentionally using a light flux that is nonconfocal with the image acquisition site of the fundus of the eye (a nonconfocal image), in an attempt to obtain information about the fundus tissue that cannot be obtained from a confocal image.
A nonconfocal AO-SLO apparatus proposed in JOSA A, VOL. 31, Issue 3, pp. 569-579 (2014) is configured to acquire a nonconfocal image of the fundus of the eye by dividing return light returning from the fundus of the eye into two or more beams on an image forming surface where the return light forms an image, entering the beams to their respective light sensors, calculating (differences among) signals of the light sensors, and imaging the fundus of the eye, in an attempt to improve the S/N ratio of the acquired two-dimensional image (blood vessel image). There is also a report in IOVS, 55, 4244-4251 (2014) of the result of using a similar imaging method in which an image of photoreceptor cells as typical eye cells was acquired that had image characteristics different from those of images observed with confocal optics systems of the related art.
Some images acquired with the nonconfocal AO-SLO apparatus described above have dependence on a particular direction in terms of sharpness, which takes form as, for example, sharpness variations between the left side and right side of a blood vessel in an acquired image. This is called the directionality of image characteristics. Taking the directionality of image characteristics into account is beneficial in an analysis of such images having the dependence. However, both of the documents cited above use an analysis method of the related art, for example, one in which pathological changes and the like of an eye to be inspected are evaluated simply by obtaining the size or density of eye cells (Japanese Patent Application Laid-Open No. 2014-198224), without taking into account the directionality of image characteristics. With this and other similar analysis methods of the related art, an image high in image characteristics dependence on a particular direction is analyzed as a nonconfocal image containing unsharp portions, which can make successful detection of, for example, photoreceptor cells difficult.